1. Field of the Invention
The present invention relates generally to a laser scanning unit, and more particularly, to such a unit having a sensor for detecting both start-of-scan and end-of-scan positions of a corresponding laser beam.
2. Description of Related Prior Art
Multi-laser color printers having a plurality of printheads are known in the prior art. Typically, each printhead generates a corresponding scanning laser beam for creating a latent image on a corresponding photoconductive drum. Each latent image is developed and may be transferred to an intermediate transfer belt so as to form a composite image, which is later transferred to a substrate. Each color image must be accurately registered relative to all of the other color images to ensure that print quality is satisfactory. During operation of the printer, the length of scan lines generated by a scanning laser beam may drift, i.e., change, resulting in its corresponding developed image being out of register with the other color images. So as to sense changing scan line length, start-of-scan and end-of-scan sensors may be associated with each laser beam.
It would be desirable if scan line length changes could be sensed without requiring costly start-of-scan and end-of-scan sensors for each laser beam in a color laser printer.